Crystallizer is a good card for Warlock, this especially if you like 5 mana 6/5s and Amethyst Spellstones. You can tap + Kobold Librarian into this for 6 mana 5/5 (+2/1) draw 2, that's pretty good. You can also hero power yourself as Bloodreaver Gul'dan if you draw this card without any other synergy and make it a 5 mana 4/5, which isn't that good but it's some tempo in the late game assuming you only did that because you drew it so late that all your synergy was used. Across all turns, you can do something to make this card not useless, making it only useless in your Gul'dan demon dead pool.